The presence of arsenic in its various chemical forms as an impurity in feed stocks and finished products can be detrimental to their use. For example, arsenic in very small quantities in a hydrocarbon stream can poison the noble metal catalysts frequently used to further process the stream by oxidation, polymerization, catalytic cracking and the like.
Since most crude oils contain arsenic in one form or another, the hydrocarbon fractions derived from cracking, fractionating or otherwise separating these raw materials will also contain arsenic. Volume concentrations of as little as one part of arsenic per million (ppm) may render some hydrocarbon streams unacceptable for further processing. For example, with present high yield catalysts for propylene polymerization, even 50 parts of arsenic per billion (ppb) in a propylene feed will poison the catalyst in a short time. For this reason, various methods of arsenic removal have been developed but improved processes are still desired.